The present invention relates to a vegetable fibre cement moulded body which utilises vegetable fibre as a reinforcing material and to a method of manufacturing the same.
Vegetable fibre cement moulded bodies, for example, vegetable fibre cement boards, are normally manufactured by kneading ligneous fibre obtained by processing wood into flakes, excelsior, wood fibre, and the like, or bamboo fibre obtained by processing bamboo in a similar manner, various types of cement, and water, and moulding this kneaded material, followed by curing and hardening of the cement. As sources of ligneous fibre, various kinds of softwood and hardwood timber are widely used. However, recent years have seen a tendency toward timber shortages, and wood conservation is also required from the viewpoint of global environmental protection. As raw materials to replace wood, bamboo materials, which grow rapidly compared to softwood and hardwood timber, and are strong and have a high degree of resiliency, have been gaining attention. However, bamboo materials contain soluble sugars, soluble resins, or the like, which are well known as substances that inhibit the hardening of cement. Therefore, in order to put into practical use materials which contain a large amount of substances that inhibit cement hardening, such as bamboo materials, as raw materials for vegetable fibre materials, an arrangement is necessary for facilitating the smooth hardening of cement.
The following methods have been conventionally proposed as methods of eliminating the cement hardening inhibition caused by the soluble sugars and resins contained in vegetable fibre materials.
For example, a method is cited wherein hardening of cement is promoted by impregnating or mixing in with the vegetable fibre materials metallic salts such as calcium chloride, magnesium chloride, aluminium chloride (Japanese Patent Laid-Open No. 51-26930, Japanese Patent Laid-Open No. 51-151722, Japanese Patent Laid-Open No. 60-118658). Furthermore, Japanese Patent Publication No. 55-14827 discloses a method of rapidly hardening and moulding a ligneous cement moulding wherein a ligneous raw material is made into fine pieces and mixed with water and ultra-rapidly hardening cement to which ferric chloride is added and mixed and then hardened and moulded by heating and pressure-fastening in the range of 90-120xc2x0 C.
In the above-described method in which a hardening acceleration agent is added, hardening of cement is performed under conditions of pressurisation and heating with the use of, for example, a hot press method, steam curing in a state of fastening, or the like. However, in a system which uses a vegetable fibre material containing a large amount of a substance that inhibits cement hardening, such as a bamboo fibre material, cement does not easily harden at ordinary temperatures, and even if the cement hardens, the strength of the resulting moulded body is extremely low. In addition, for metallic salts used as hardening acceleration agents, chloride types are commonly used; in cases where a chloride-type hardening acceleration agent is used in a construction material, there is a fear that metallic parts such as screws for fastening will rust at the time of constructing the resulting moulded body, and that metallic parts of kneading machines, iron plates for moulding, and the like, will rust at the time of producing the moulded body. In a system wherein a vegetable fibre material containing a large amount of a substance that inhibits cement hardening is used, there is also a fear that since hydration of the cement is markedly delayed, these hardening acceleration agents will not work effectively.
Another method is cited wherein resin portions within excelsior are removed in advance by soak-treating it in river water, sea water, and/or a chemical solution, and using the resulting excelsior (Japanese Patent Laid-Open No. 55-164054). Here, it is stated that, in order to remove the resin portions within the excelsior raw material to an extent which does not adversely affect the production of the excelsior cement boards, it is necessary to pre-soak the excelsior in water for 2 to 10 hours, depending on the type of resin, using mainly cold water in the range of 1 to 45xc2x0 C. In this case, since a long period of time is required for the soaking treatment, it cannot be denied that there is a reduction in productivity. Moreover, in order to obtain stable product quality, a long period of time is required for soaking, and there is an apprehension that the product quality will vary depending on the type of wood used. Furthermore, Japanese Patent Publication No. 61-4784 discloses a method of manufacturing a ligneous cement board characterised in that the ligneous material is treated beforehand with a salt having 1 or more sulphate radicals selected from the group consisting of magnesium sulphate, calcium sulphate, aluminium sulphate and zinc sulphate, calcium hydroxide and/or calcium carbonate, and 1 or more carboxylic acids selected from the group consisting of formic acid, acetic acid, and oxalic acid, and cement is then mixed in. Moreover, Japanese Patent Publication No. 61-5422 discloses a method of manufacturing a ligneous cement board characterised in that a treatment for preventing the inhibition of the cement hardening of a ligneous material is performed with an aluminium salt of a strong acid and an acetate, and the ligneous material which has undergone this cement hardening inhibition treatment is used to manufacture the ligneous cement board. These treatments all bring about an increase in the cost of the draining process for soaking treatment solutions and in running costs.
There is also a method wherein a substance that inhibits cement hardening in a ligneous material is made insoluble by treatment with paraformaldehyde or formalin (Japanese Patent Laid-Open No. 50-127925). However, the pharmaceuticals used in this method are dangerous, and expenses are incurred for chemical waste treatment facilities, work site, environment facilities and the like, which leads to an increase in costs.
Furthermore, Japanese Patent Publication No. 5-65455 discloses a method of manufacturing a ligneous cement board by kneading a ligneous material, cement and water to form a mixed mat, then moulding the mixed mat by pressure-fastening, and curing and hardening, wherein a metallic compound comprising 1 or more substances selected from sulphates, chlorides, or hydroxides of iron, copper, zinc or lead is mixed into the kneading water, and the metallic compound is bonded to a component extracted from the ligneous material to form a highly stable complex, thereby preventing cement hardening inhibition due to the extracted component.
Furthermore, Japanese Patent Laid-Open No. 8-2954 discloses a method of treating a ligneous reinforcing material characterised in that a surface of the ligneous reinforcing material is coated with calcium carbonate by adding to and mixing in the ligneous reinforcing material calcium hydroxide and bicarbonate of an alkali metal and/or ammonia and heating.
The above-mentioned conventional technologies are methods which prevent substances that inhibit hardening from diffusing into cement by causing gelling to start while the amount of the substances which inhibit cement hardening (soluble sugars and resins, and the like) being eluted from a vegetable fibre material which has been mixed in a mixture of raw materials as a reinforcing material is relatively small, or a method which prevents substances that inhibit cement hardening from being eluted into the cement by pretreating the vegetable fibre material for reinforcement with a chemical. However, in cases where bamboo fibre and the like, which contains a large amount of soluble sugars and resins, as compared to such ligneous fibre materials for reinforcement as softwood and hardwood timber, is used as a vegetable fibre material for reinforcement, since there is a possibility that the soluble sugars and resins will be eluted before the cement hardens, there is a fear that the hardening of the cement will be inhibited. Even if a hardening acceleration agent is added in cases where the hardening is inhibited, it is difficult to revert the delayed hydration reaction back to normal. Moreover, it is difficult to completely coat the surface of these vegetable fibre materials with chemicals and the like, and the inadequacy of the coating, similar to the above-mentioned case, leads to the apprehension that the hardening will be inhibited. It has thus been difficult to obtain a stable product of high quality.
On the other hand, current production of vegetable fibre cement moulded bodies generally has the steps of: mixing at least vegetable fibre material, cement and water as the main raw materials; moulding the mixed raw material on a template; placing in multiple layers a complex of this moulded body and the template, which are fastened together while being pressurised; curing while fastened until handling of the moulded body becomes possible; and unfastening to separate the moulded body and the template (hereinafter referred to as detachment); and this method is frequently employed at present. In order to perform detachment, it is necessary for the moulded body to possess shape retention properties and the strength to withstand the handling. The reason for placing the moulded raw material in multiple layers is that, since it is normal for xe2x80x9ctime required to mould one moulded body less than  less than time required for 1 cycle of pressurisation/fasteningxe2x80x9d, it is desirable to achieve xe2x80x9ctime required to mould one moulded body x no. of layersxe2x89xa7time required for 1 cycle of pressurisation/fasteningxe2x80x9d in order to manufacture moulded bodies efficiently. Moreover, fastening one on one, or a small number of layers requires an extremely large number of pieces of fastening equipment, which is unrealistic.
However, if the placing in multiple layers takes time, the cement hardening reaction of the material which has been moulded on the template earlier proceeds before the pressure-fastening, which results in the strength of the manufactured vegetable fibre cement moulded body being low (the strength of the vegetable fibre cement moulded body only manifests when the cement is caused to undergo hydration reaction while being pressure-fastened). Furthermore, in a case where the step of placing in multiple layers is interrupted due to some trouble, the operational time is further increased. In particular, in cases where a cement hardening acceleration agent is used, as conventionally proposed, if the placing in multiple layers takes time, the cement hardening reaction proceeds before the pressure-fastening, which results in the manufactured moulded body having markedly insufficient strength.
The object of the present invention is therefore to provide a vegetable fibre cement moulded body of high strength which is not easily affected by substances which inhibit cement hardening and a method of manufacturing it efficiently and at low cost.
Another object of the present invention is to provide, in the manufacture of vegetable fibre cement moulded bodies as frequently employed at present such as described above, a method of manufacturing a vegetable fibre cement moulded body wherein the cement hardening reaction of a material placed on a template does not easily proceed before pressure-fastening, the curing time required from the completion of the fastening up to the detachment step is reduced, the metallic equipment parts involved in the manufacturing of the moulded body are not corroded, and which is low in cost.
The present inventors have succeeded in solving the above conventional problems as a result of strenuous research.
That is to say, the present invention provides a vegetable fibre cement moulded body including at least a vegetable fibre material and cement characterised in that the vegetable fibre cement moulded body contains a nitrate as an additive agent.
Furthermore, the present invention provides a vegetable fibre cement moulded body as aforementioned wherein the nitrate content is 0.5-10% by weight relative to the total amount of solid raw material.
Moreover, the present invention provides a vegetable fibre cement moulded body as aforementioned wherein the nitrate is 1 or more kinds selected from the group consisting of magnesium nitrate, ferric nitrate, nickel nitrate and aluminium nitrate.
In addition, the present invention provides a method of manufacturing a vegetable fibre cement moulded body including a step of mixing a raw material that includes at least a vegetable fibre material, cement and water, a step of moulding the mixed material, and a step of curing this moulded body, characterised in that a nitrate is added at the time of the aforementioned raw material mixing step or the aforementioned moulding step.
Furthermore, the present invention provides a manufacturing method as aforementioned wherein the nitrate is added in the form of an aqueous solution.
Moreover, the present invention provides a method of manufacturing a vegetable fibre cement moulded body including a step of mixing a raw material that includes at least a vegetable fibre material, cement and water, a step of moulding the mixed material on a template, a step of stacking multiple layers of composites of this moulded body and the template, a step of pressurising as well as fastening while under pressurisation the aforementioned stacked multiple layers of composites, a step of curing the fastened moulded bodies until their handling becomes possible, and a step of unfastening and separating the aforementioned moulded bodies and templates, characterised in that a nitrate is added at the time of the aforementioned raw material mixing step or moulding step and that a heat treatment is implemented for the moulded bodies in the aforementioned curing step.
Furthermore, the present invention provides a manufacturing method as aforementioned wherein the heat treatment is performed at a temperature between 50xc2x0 C. or more and less than 100xc2x0 C.
Moreover, the present invention provides a manufacturing method as aforementioned wherein the heat treatment is performed at a temperature of 60-80xc2x0 C.
In addition, the present invention provides a manufacturing method as aforementioned wherein the heat treatment is steam curing.
Furthermore, the present invention provides a manufacturing method as aforementioned wherein ordinary curing is performed before the heat treatment.
Moreover, the present invention provides a manufacturing method as aforementioned wherein secondary curing of the moulded bodies separated from the template is performed by ordinary curing.